In recent years, as a wafer which is highly useful for a bipolar device and a power device, a relatively thick thick-film SOI wafer with an SOI layer having a film thickness of several μm to several-ten μm has been greatly expected.
However, when manufacturing a high-quality SOI wafer that is required to have an SOI layer having a film thickness of several μm and a thickness tolerance of about ±0.1 μm by using wafers bonding method, the method for reducing a film thickness of a bond wafer (a wafer for forming an SOI layer) by grinding/polishing can obtain radial uniformity of at most about ±0.3 μm only with respect to a target film thickness even though a highly accurate polishing technique is utilized, irregularities in film thickness of the SOI layer are considerable, and there is a limit to the film thickness uniformity.
Therefore, as a method for realizing this, there is Patent Document 1. In this Patent Document 1, a thin SOI layer is formed by the ion implantation delamination method that can relatively easily obtain the film thickness uniformity of SOI layer that is ±0.01 μm or less, and epitaxial growth is then performed on this SOI layer, whereby the thickness of the SOI layer is increased.
However, in this case, when an SOI wafer is fabricated by forming an oxide film on a base wafer (a wafer which becomes a support wafer) in advance and performing bonding with consideration given to the warpage of the SOI wafer, since the oxide film in a peripheral terrace portion (the unbonded portion) of the SOI wafer is in an exposed state, if epitaxial growth is performed on the entire surface of an SOI layer in this state, polysilicon grows on the oxide film in the terrace portion, causing particle contamination or the like in subsequent processes.
In general, to prevent the growth of the polysilicon, epitaxial growth is performed after removing the oxide film in the terrace portion by immersing the SOI wafer in an aqueous HF solution. However, when a back surface oxide film for preventing warpage is left on the base wafer, since the film thickness of the back surface oxide film is also reduced, larger warpage occurs in an SOI wafer to be manufactured.
To solve such a problem, there is a method by which epitaxial growth is performed after completely removing only the oxide film in the terrace portion by a method such as performing HF spin cleaning as in Patent Document 2 to prevent the back surface oxide film for preventing warpage in the SOI wafer from being unnecessarily reduced.